The neural and behavioral correlates of the 4- and 8-month-old infant's ability to distinguish between frequently and infrequently presented familiar and novel events was examined. Cortical event-related potentials (ERPs) were recorded as infants were familiarized to two faces. During the test trials that followed, one of these faces was presented frequently, and the other infrequently; on each of the remaining 20% of the trials, a previously unseen, novel face was presented. Following the ERP phase, infants' looking times were recorded to pairs of faces, some of which had been seen during the ERP testing, and some of which had not. At 4 months the ERP activity invoked by the three classes of events was similar, suggesting that infants were unable to distinguish among them. At 8 months the ERP activity differed only between the Infrequent Novel events and the two classes of familiar events, but did not differ between the frequently and infrequently presented familiar events. The ERP findings complement previously reported data from 6-month-old infants in describing a trend whereby infants become increasingly able to respond to stimuli on the basis of whether they have been seen before, and not on the basis of how often they had been seen. The behavioral data at both 4 and 8 months were less clear cut than the ERP data. These findings are discussed in the context of the neural and cognitive processes involved in dissociating probability information from novelty detection.
Bibliographical noteFunding Information:
Research and manuscript preparation were made possible in part by grants to the first author from the NIH (HD23389), the McKnight-Land Grant endowment of the University of Minnesota, and by a training grant from the NIH (HDO7151) to the Center for Research in Learning, Perception, and Cognition, University of Minnesota. The authors thank the infants who participated in this study, Terri Kuczmarski and Leesa Slater for assisting in data collection, Kim Pearson for programming, and Merv Bergman for technical assistance. Particular thanks is extended to Mary Smith-Henschel for testing subjects and overseeing portions of the project. A preliminary report of this work was presented at the 1990 meetings of the International Conference on Infant Studies (Montreal, Canada). Reprint requests should be sent to Charles A. Nelson, Institute of Child Development, University of Minnesota, 51 East River Road, Minneapolis, MN 55455.